1. Field of the Invention
The present invention relates to a solar energy collecting system which can be used to heat residential, commercial, or industrial buildings and to power an absorption cooler to air condition such buildings. Further, energy collected by this system can be converted to other forms for many different uses.
Recent experience has demonstrated that the earth's natural energy resources are limited and as supplies of once plentiful energy sources such as petroleum dwindle, their cost increases rapidly. Furthermore, the costs of still relatively abundant energy resources such as coal have also increased because of the environmental impact of recovering them in usable form and because of the relative lack of abundance of types and grades which can be used without severe environmental repercussions. Still other natural energy resources like nuclear and geothermal power require enormous capital as well as lead-time to make them practical on a large scale. Moreover, the environmental ramifications of their use is not yet fully understood or appreciated.
These and other factors have intensified the search for sources of energy alternative to those in common use today. For many reasons, solar energy is a primary target of this investigation. First, it is for all intents and purposes, inexhaustible. Second, it is abundant. The total energy consumed in the United States in
1970 WAS EQUIVALENT TO THE ENERGY OF SUNLIGHT RECEIVED BY 4300 SQUARE MILES OF LAND, THAT IS, ONLY 0.15 PERCENT OF THE TOTAL LAND AREA OF THE CONTINENTIAL United States, in that same year, J. R. Williams, "Solar Energy, Technology and Applications", p. 3, (1974). Moreover, the spiralling costs for energy from presently tapped sources has made solar energy economically feasible. Thus, the NSF/NASA Solar Energy Panel has concluded that three broad applications for solar energy are "most promising from technical, economic, and energy quantity standpoints. These are: (1) the heating and cooling of residential and commerical buildings, (2) the chemical and biological conversion of organic materials to liquid, solid, and gaseous fuels, and (3) generation of electricity." The Panel has also concluded that "solar energy can be developed to meet sizable portions of the Nation's future energy needs." P. Donovan and W. Woodward, "An Assessment of Solar Energy as a National Energy Resource", NSF/NASA Solar Energy Panel (University of Maryland, December 1972).
2. Description of the Prior Art
Systems for collecting solar energy, which have been developed in response to the search for alternative sources of energy, can be categorized in three basic ways, namely, (1) flat plate collectors with no provision for concentration of the sun's radiant energy on them, (2) medium performance radiation concentrating collectors which utilize, for example, a parabolic cylinder to focus the sun's radiant energy on a heat exchange device such as a collector pipe through which water circulates, and (3) high performance radiation concentrating collectors which utilize parabolic concentrators or concentrators composed of many flat mirrors focused on the same point, J. Williams, "Solar Energy, Technology and Applications", p. 17, (1974).
Flat plate collectors are ordinarily used to heat a fluid medium such as circulating water which is, in turn, used to heat or cool buildings or to heat water for use in those buildings. Typically, these collectors include a plate having a radiation absorbing coating which forms the bottom of an insulated box. A transparent window of glass or plastic, which tends to be opaque to infrared radiation and to retard convective heat transfer inside the box, transmits sunlight to the absorbing plate which is then heated. The fluid medium is circulated under, through, or over the plate where it consequently is heated. See, for example, U.S. Pat. Nos. 3,387,602; 3,369,539; 3,236,294; and 3,215,134, all to H. E. Thomason. However, these flat plate collctors achieve a maximum efficiency of about only 60 percent at relatively low outlet temperatures.
Solar radiation concentrating systems are used to produce higher temperatures. The focus of the concentrator is usually maintained on a heat exchange unit by making one or the other movable in an attempt to achieve maximum performance. For example, U.S. Pat. Nos. 3,254,643 and 3,270,739 both to Thomason and U.S. Pat. No. 3,841,302 to G. Falbel disclose systems having fixed radiation collectors, but having reflectors or concentrators which include at least a portion that is movable. However, provision of movable reflectors or collectors adds to the complexity and, hence, expense of the systems. These patents also suggest that the reflectors can be used to protect the collectors from the elements as well as to reradiate energy back toward the sky to achieve a cooling effect.
U.S. Pat. No. 2,625,930 (Harris) discloses a system which employs a series of parallel reflectors which focus sunlight through a complementary series of windows to be transmitted to hollow beams that contain a heat absorbing medium. However, maintenance of this structure is difficult since the beams are not readily accessible from the upper surface of the reflector nor are the reflectors themselves readily accessible. Further, this system is designed to reflect solar radiation away from the windows and, hence, the hollow beams in the summer.
U.S. Pat. No. 3,232,795 (Gillette et al.) discloses a system which employs wedge-shaped reflectors to concentrate solar radiation on solar cells mounted horizontally between the reflectors. The system, intended for use in outer space, can then generate electricity. This system's primary objectives are to fully illuminate the solar cells while dissipating heat about them. The cells may be faced toward the sun at anytime.
Known solar energy collecting systems of the types described above have certain drawbacks. Simple flat plate energy collectors have limited efficiency and low outlet temperatures. Maintenance of collectors and reflectors of more complicated systems is made difficult by the limited access which is provided to their components. Perhaps more importantly, however, these more complex systems are designed to generate usable energy only on a limited seasonal basis. With the exception of the Gillette device which is designed for use in space, each is constructed to dissipate or to avoid collection of solar energy during at least a portion of the year, usually summer, to prevent heat from being accumulated by a collector. Thus, certain designs shield the collector during the summer; others reflect the sun's energy away from the collector at that time. In both cases, the collector is effectively turned off and not utilized, thus, greatly decreasing the overall year-long operating efficiency of the system.